1. Field of the Invention
The present invention relates to an original illuminating apparatus for use in electrophotographic copying machine, original reader of facsimile equipment and other image processing apparatus in which a desired image is formed from an original.
2. Description of the Prior Art
Conventional original illuminating apparatus have a common problem that the atmospheric temperature in the image processing apparatus and/or the temperature of platen glass are undesirably raised up by heat radiated from the light source. This problem is of critical importance in particular when a light emission filament, such as halogen lamp, is used as the original illumination light source in order to obtain a large quantity of light from the light source. For example, there is known a type of apparatus in which the platen glass is formed in the shape of a slit-like window and is fixed in a position whereas the original is moved across the glass platen for scanning the original which is illuminated by a lamp stationary relative to the glass platen. When a large number of originals are continuously fed into such an apparatus and the lamp continues to be on for a long time, then an abnormal temperature rise of the platen glass is caused by the radiation heat from the lamp. In such a case, the original is subjected to quality change. If the original is a thin sheet, it is dried up rapidly and its physical properties such as elasticity and smoothness are greatly changed so that the trouble of paper jamming may frequently be produced. Furthermore, if the operator unintentionally touches the heated platen glass, it may cause a burn in this hand.
To prevent the above troubles, in many of the conventional apparatus, the platen glass, lamp and reflector tube have been cooled by means of cooling air. However, it has various drawbacks. First, it is difficult to attain uniform cooling. Second, to obtain an adequate cooling effect, the apparatus is required to have a larger size.
Japanese Patent Application laid open No. Sho.55-95937 has disclosed such an apparatus in which the reflector for original illumination light is cooled not by cooling air but by means of a heat pipe. This apparatus has been proposed and is directed at reducing the temperature elevation of the atmosphere and therefore reducing also the temperature elevation of the platen glass by cooling the reflector. It is admitted that this apparatus has an effect to prevent the temperature elevation of the platen glass through the atmosphere. However, the temperature of the platen glass rises up not only through the atmosphere but also directly by thermal rays radiated together with visible light from the lamp. Therefore, even in the prior art apparatus, abnormal temperature rising of glass platen is caused by radiation heat when the apparatus operates continuously for a long time.